Semiconductor light emitting devices can be utilized as light sources for use in vehicles (see, for example, Japanese Patent Application Laid-Open Nos. 2005-322923 and 2008-507850). General semiconductor light emitting devices can include a light emitting device having an LED element and a phosphor for wavelength-converting light emitted from the LED element in combination, and can have a structure wherein a layer in which the phosphor is dispersed (wavelength conversion layer) is deposited on the LED element. A semiconductor light emitting device with the above configuration can provide a luminance distribution which is formed on a light emission surface and in which the luminance gradually decreases from the center of the surface of the wavelength conversion layer as its maximum luminance toward the periphery or a uniform luminance distribution within the light emission surface.
As to a vehicle headlamp, a cut-off line can be formed in the light distribution pattern to prevent the vehicle from directly projecting light to an opposite vehicle (driver). In order to form a clear cut-off line in the light distribution pattern, the maximum luminance portion of the light distribution pattern formed by the light source can be disposed on or near the cut-off line. When the semiconductor light emitting device with the above luminance distribution in which the luminance gradually decreases toward the periphery is used in the above vehicle headlamp, the conventional vehicle headlamp should include a shade or the like to cut and/or block half of the light in the luminance distribution, thereby forming the clear cut-off line. In this case, however, the light utilization efficiency may deteriorate.
Furthermore, in order to form a light distribution pattern with a high far-distance visibility, it is possible to form a luminance gradation where the luminance (brightness) is decreased gradually from the cut-off line to the lower side on a virtual screen in front of the vehicle. In this case, if a semiconductor light emitting device with a uniform luminance distribution is used, formation of the luminance gradation is difficult.